Microelectromechanical apparatus for elevating and tilting a platform

ABSTRACT

A microelectromechanical (MEM) apparatus is disclosed which has a platform that can be elevated above a substrate and tilted at an arbitrary angle using a plurality of flexible members which support the platform and control its movement. Each flexible member is further controlled by one or more MEM actuators which act to bend the flexible member. The MEM actuators can be electrostatic comb actuators or vertical zip actuators, or a combination thereof. The MEM apparatus can include a mirror coating to form a programmable mirror for redirecting or switching one or more light beams for use in a projection display. The MEM apparatus with the mirror coating also has applications for switching light beams between optical fibers for use in a local area fiber optic network, or for use in fiber optic telecommunications or data communications systems.

CROSS REFERENCE TO RELATED INVENTIONS

This application claims the benefit of U.S. Provisional Application No.60/196,622 filed Apr. 11, 2000.

GOVERNMENT RIGHTS

This invention was made with Government support under contract No.DE-AC04-94AL85000 awarded by the U.S. Department of Energy. TheGovernment has certain rights in the invention.

FIELD OF THE INVENTION

The present invention generally relates to microelectromechanicaldevices and in particular to a microelectromechanical apparatus having aplatform which can be elevated and tilted, for example, to form amicromirror for redirecting or switching an incident light beam. Thepresent invention has applications for forming an array of tiltablemicromirrors for use in switching light beams between a plurality ofinput optical fibers and a plurality of output optical fibers, or forforming a projected light display.

BACKGROUND OF THE INVENTION

The use of fiber optics for data communications and telecommunicationsis desirable to increase the bandwidth for information transmission.Lasers used for fiber optics communications produce light that can bemodulated at rates up to many tens of Gigahertz (GHz). Multiple laserbeams can also be wavelength division multiplexed for transmissionthrough a single optical fiber. Presently, a limitation in informationtransmission with fiber optics is in routing of optical signals (i.e.modulated light) between different fibers. Thus, the need exists foroptical switching technology to redirect the optical signals or portionsthereof from one optical fiber to any of up to hundreds or more otheroptical fibers.

Surface micromachining, which can be used to build-upmicroelectromechanical systems (MEMS) layer by layer, is a promisingtechnology for forming such optical signal routers (i.e. switches). Thepresent invention is directed to a platform supported by two or threecompliant elevation structures so that the platform can be tilted in anarbitrary direction to form in combination with an optical coatingdisposed thereon an optical switch which can be used for fiber opticssignal routing, or for redirecting incident light beams for otherapplications such as projection displays.

An advantage of the present invention is that control of the tilt angleof the platform can be achieved by independently controlling one or morecompliant elevation structures, thereby providing precise angularpositioning of the platform over large tilt angles (e.g. ±20 degrees).

Another advantage of the present invention is that the use of compliantelevation structures to elevate and/or tilt the platform eliminatesrubbing surfaces and thereby decreases or prevents wear-induced changesin performance over time.

A further advantage of the present invention is that the platform can beelevated or tilted with negligible stress or deformation of the platforminduced by the compliant elevation structures.

Yet another advantage of the present invention is that the platform canbe elevated without tilting by operating a plurality of the compliantelevation structures in unison. Such an elevatable platform can be used,for example, to control the focal plane of a focusing lens within anoptical data storage device to within a fraction of a micron.

These and other advantages of the present invention will become evidentto those skilled in the art.

SUMMARY OF THE INVENTION

The present invention relates to a microelectromechanical (MEM)apparatus, comprising a substrate; a platform (i.e. a stage) supportedabove the substrate by a trio of flexible members; and means for bendingeach flexible member, thereby changing the elevation or tilt of theplatform. The substrate generally comprises silicon (e.g. a siliconwafer or portion thereof); and the platform generally comprisesmonocrystalline or polycrystalline silicon.

Each flexible member is equidistantly spaced about the platform and canbe anchored to the substrate directly, or through another element towhich the flexible member is connected. The other end of each flexiblemember can be operated independently of other flexible memberssupporting the platform thereby enabling the platform to be tilted.Alternately, the flexible members can be operated in unison to elevatethe platform above the substrate while maintaining the platformsubstantially coplanar with the substrate.

The connection of each flexible member to the platform is preferablymade using a compliant member. In some embodiments of the presentinvention, the compliant members connect a point near the midpoint ofeach flexible member to an outer edge (i.e. the periphery) of theplatform. In other embodiments of the present invention, one end of eachcompliant member is connected proximate to an end of one of the flexiblemembers; and the other end of each compliant member is connected to theplatform at a point equidistant from a central axis of the platform(i.e. between the central axis and the outer edge of the platform).

The platform can have an arbitrary shape (e.g. circular or polygonal),and can further be either planar or curved (e.g. with an upper surfacecurved inward). The platform can also have a mirror coating on a surfacethereof (e.g. the upper surface which is also termed herein as thetopside) for reflecting an incident light beam. When a mirror coating isprovided, the other surface of the platform can include astress-compensation coating formed thereon, if needed, to compensate forany stress induced in the platform by the mirror coating which mightotherwise distort the topography of the platform.

The means for bending each flexible member and thereby elevating ortilting the platform can comprise a microelectromechanical (MEM)actuator (e.g. an electrostatic actuator) which is operatively connectedto the flexible member. In some embodiments of the present invention,each electrostatic actuator can comprise an electrostatic comb actuatorwhich further comprises a plurality of stationary electrostatic combsattached to the substrate and a plurality of moveable electrostaticcombs attached to a frame supported above the substrate, with themoveable electrostatic combs being moveable towards the stationaryelectrostatic combs in response to an actuation voltage (i.e. anelectrical signal) provided therebetween. Each electrostatic combfurther comprises a plurality of spaced fingers, with the fingers ofeach moveable electrostatic comb being enmeshed with the fingers of anadjacent stationary electrostatic comb.

In other embodiments of the present invention, each electrostaticactuator can comprise a vertical zip actuator which further comprises atleast one first electrode supported on the substrate and a secondelectrode superposed above the first electrode with a spacing betweenthe first and electrodes being variable along the length of thesuperposed first and second electrodes, and with the second electrodebeing moveable towards the first electrode in response to an actuationvoltage provided therebetween. One end of the second electrode can beconnected to the flexible member, and the other end of the secondelectrode can anchored to the substrate (e.g. through a mechanicallatch). In some cases, the vertical zip actuator can be segmented toprovide a plurality of separately-connected first electrodes, forexample, to allow portions of the vertical zip actuator to be separatelyaddressed for precise and repeatable control of the elevation or tilt ofthe platform.

In some embodiments of the present invention, each flexible member thatis connected to the compliant member can be further connected to a pairof elongate elevation members juxtaposed on both sides of the flexiblemember, with the elevation members being anchored to the substrate (e.g.through a flexible joint).

To initially elevate the platform above the substrate after fabricationand release thereof, a plurality of pre-stressed members can be providedunderneath the platform, with each pre-stressed member being anchored atone end thereof to the substrate, and with the other end of eachpre-stressed member providing a force on the platform to urge theplatform upward from the substrate. Each pre-stressed member cancomprise an oxide material (e.g. silicon dioxide or a silicate glass)encased within a polysilicon body for producing a stress gradient in thepre-stressed member.

A plurality of restraining clips can also be optionally used for holdingthe platform in place during fabrication thereof, with the restrainingclips being moveable away from the platform to release the platform formovement thereof. Alternately, a plurality of fuses (e.g. comprisingpolycrystalline silicon) can be provided to anchor the platform to thesubstrate during fabrication thereof, with each fuse being electricallyseverable to release the platform for movement.

The present invention is also related to a microelectromechanicalapparatus comprising a substrate; a platform supported above thesubstrate by a plurality of flexible members, with each flexible memberbeing connected to the platform at a point between a central axis of theplatform and the periphery of the platform; and a plurality ofelectrostatic actuators providing movement in a direction substantiallyin the plane of the substrate, with each electrostatic actuator beingoperatively connected to one of the flexible members to bend theflexible member out of the plane of the substrate, thereby elevating ortilting the platform. A mirror coating can be provided on the platformfor reflecting an incident light beam.

Additionally, the present invention relates to a microelectromechanicalapparatus comprising a substrate (e.g. comprising silicon); a platformformed on the substrate and having a central axis oriented at an angle(e.g. 90°) to the plane of the substrate; a plurality of compliantmembers, each connected at a first end thereof to an underside of theplatform (e.g. at a point equidistant from the central axis), with theplurality of compliant members further being arranged symmetricallyabout the central axis; a plurality of elongate flexible members, eachconnected at an inner end thereof to a second end of one of thecompliant members, with an outer end of each elongate flexible memberbeing operatively connected to an electrostatic actuator; and at leastone elongate elevation member connecting each flexible member to thesubstrate. Each elevation member acts in combination with the flexiblemember to which the elevation member is connected to elevate or tilt theplatform in response to a force provided on the outer end of theflexible member by the electrostatic actuator. Generally, the pluralityof flexible members comprises a trio of flexible members.

The platform can be, for example, either circular or polygonal and caninclude a mirror coating on a topside thereof. If needed, astress-compensation coating can be deposited on the underside of theplatform to compensate for any stress induced in the platform by themirror coating. The apparatus can further include a plurality of fusesor restraining clips for securing the platform to the substrate, withthe fuses being electrically severable and the restraining clips beingremovable to release the platform for movement.

To aid in elevating the platform, a plurality of pre-stressed memberscan be located beneath the platform, with each pre-stressed member beinganchored at one end thereof to the substrate, and with the other end ofeach pre-stressed member providing an upward force on the underside ofthe platform to urge the platform away from the substrate. Thepre-stressed members can be elongate, and can be oriented along a linefrom the central axis. In such arrangement, each pre-stressed member canbe anchored to the substrate at a point proximate to the central axis.

The present invention is further related to a microelectromechanicalapparatus that comprises a substrate (e.g. comprising silicon); aplatform supported above the substrate by a plurality (e.g. two orthree) of elongate flexible members; at least one elevation memberconnected at one end thereof to each flexible member, with the other endof the elevation member being anchored to the substrate through aflexible joint; and an electrostatic actuator operatively connected tothe other end of each flexible member to provide a force to the flexiblemember, thereby flexing the flexible member and elevatating or tiltingthe platform. The flexible members can be spaced by an angle of 120degrees (120°) about a central axis of the platform. Each flexiblemember preferably supports the platform by a compliant member whichconnects the flexible member to the platform. For redirecting anincident light beam, the platform can include a mirror coating on atopside thereof. When two flexible members are used, the platform can beanchored on one side thereof to the substrate by a flexible hinge.

Finally, the present invention is related to an apparatus forredirecting an incident light beam that comprises a mirror supportedabove a substrate for reflecting the incident light; and a trio ofelectrostatic actuators spaced about a central axis of the mirror andoperatively connected to tilt the mirror in response to an actuationvoltage provided to at least one of the trio of electrostatic actuators.The substrate can comprise silicon; and the mirror can comprisepolycrystalline silicon. The mirror comprises a platform with alight-reflective coating thereon, with the platform being planar to forma planar mirror (i.e. a flat mirror), or with the platform being curvedto form a curved mirror (e.g. a spherical mirror).

Each electrostatic actuator can be operatively connected to the mirrorthrough a flexible member which is bendable out of the plane of thesubstrate. A compliant member can also be located between each flexiblemember and the mirror to connect each compliant member to the mirror ata point at the periphery of the mirror or between the periphery and thecentral axis of the mirror. A displacement multiplier can also belocated between the electrostatic actuator and the flexible member.

Additional advantages and novel features of the invention will becomeapparent to those skilled in the art upon examination of the followingdetailed description thereof when considered in conjunction with theaccompanying drawings. The advantages of the invention can be realizedand attained by means of the instrumentalities and combinationsparticularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a partof the specification, illustrate several aspects of the presentinvention and, together with the description, serve to explain theprinciples of the invention. The drawings are only for the purpose ofillustrating preferred embodiments of the invention and are not to beconstrued as limiting the invention. In the drawings:

FIG. 1A shows a schematic plan view of a first embodiment of theapparatus of the present invention.

FIG. 1B shows a schematic side view of the first embodiment of theapparatus in FIG. 1A to illustrate operation of the flexible member forelevating or tilting the platform.

FIG. 1C shows a schematic side view of the first embodiment of theapparatus in FIG. 1A with an optional mirror coating provided on atopside of the platform.

FIG. 1D shows a schematic cross-section view of the first embodiment ofthe apparatus in FIG. 1A along the section line 1—1 to illustrateformation of an opening through the substrate for depositing astress-compensation coating on an underside of the platform.

FIG. 2A shows a schematic plan view of an optional pry bar that can beused to initially elevate the platform in FIG. 1.

FIGS. 2B and 2C show schematic cross-section views along the sectionline 2—2 in FIG. 2A to illustrate operation of the pry bar for initiallyelevating the platform.

FIGS. 3A and 3B schematically illustrate a second embodiment of thepresent invention in plan view and in side view, respectively.

FIG. 4 schematically illustrates in plan view a third embodiment of thepresent invention.

FIG. 5A shows a schematic cross-section view along the section line 3—3in FIG. 4 to illustrate details of the platform and the attachment ofthe flexible member to the platform using a compliant member.

FIG. 5B schematically illustrates an alternate connection of theflexible members to the platform using a sub-platform.

FIG. 6 shows an enlarged schematic plan view of the MEM actuator in FIG.4.

FIGS. 7A and 7B show schematic cross-section views along the sectionline 4—4 in FIG. 6 to illustrate use of the MEM actuator to change theelevation of flexible member and elevation members, thereby elevating ortilting the platform.

FIG. 8A shows a schematic plan view of a pre-stressed member duringfabrication thereof, including a cut-away view showing the body and coreof the pre-stressed member.

FIG. 8B shows a schematic side view of the pre-stressed member of FIG.8A during fabrication.

FIG. 8C shows upward bending of the pre-stressed member due to a stressgradient therein after removal of the surrounding sacrificial oxide.

FIG. 9A shows a schematic cross-section view along the section line 5—5in FIG. 4 to illustrate attachment of the platform to the substrateusing a fuse.

FIG. 9B illustrates release and upward movement of the platform of FIG.9A after electrical severing of the fuse.

FIG. 10A shows a schematic cross-section view of a restraining clip forattaching the platform to the substrate.

FIG. 10B illustrates release and upward movement of the platform of FIG.10A after disengaging the restraining clip.

FIG. 11 shows a schematic plan view of a fourth embodiment of thepresent invention.

FIG. 12A shows an enlarged plan view of the vertical zip actuator ofFIG. 11 prior to engagement of a mechanical latch to elevate theflexible member and elevation members.

FIG. 12A shows an enlarged plan view of the vertical zip actuator ofFIG. 11 with the mechanical latch engaged to elevate the flexible memberand the elevation members for operation of the apparatus.

FIGS. 13A and 13B show schematic cross-section views along the sectionline 6—6 in FIG. 12B to illustrate use of the vertical zip actuator tochange the elevation of flexible member and elevation members, therebyelevating or tilting the platform.

FIG. 14A shows a schematic plan view of an alternative contact-freevertical zip actuator.

FIGS. 14B and 14C illustrate operation of the contact-free vertical zipactuator of FIG. 14A.

FIG. 15A shows a schematic plan view of a fifth embodiment of thepresent invention.

FIG. 15B shows a side view of the device of FIG. 15A after engagement ofthe mechanical latches to elevate the platform.

FIG. 15C shows a side view of the device of FIGS. 15A and 15B afterapplying an actuation voltage to the vertical zip actuator to change theelevation on one side of the platform.

FIGS. 16A and 16B show a schematic plan view and a side view,respectively, for a sixth embodiment of the present invention.

FIG. 17 shows a seventh embodiment of the present inventionincorporating features from the devices of FIGS. 4 and 11.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, there is shown a schematic plan view of a firstembodiment of the microelectromechanical (MEM) apparatus 10 of thepresent invention. The apparatus 10 comprises a substrate 12, a platform14 supported above the substrate by a plurality of flexible members 16,and means for bending each flexible member to elevate or tilt theplatform 14. In FIG. 1, the bending means is indicated by a plurality ofarrows which show the directions of applied mechanical actuation forceswhich can be generated by MEM actuators 18 which will be described indetail hereinafter (see FIGS. 3A and 3B, and FIGS. 15A-15C). In FIGS. 1Aand 1B, the actuation forces are generally directed substantially in theplane of the substrate 12, but act to bend each flexible member 16 anddisplace the member 16 out of the plane of the substrate 12. In otherembodiments of the present invention, the actuation forces can bedirected substantially normal to the plane of the substrate 12 to bendand displace the flexible member 16 in a direction that is out of theplane of the substrate 12 (see FIGS. 15A-15C). Although, the MEMactuator 18 will be described hereinafter as an electrostatic actuator,those skilled in the art will understand that other types ofsurface-micromachined actuators can be substituted for the electrostaticactuator, including thermal actuators and electrostatic micromotors.

In FIG. 1B, the mechanical forces provided to the flexible members 16result in an upward displacement of the members 16 out of the plane ofthe substrate 12. This elevates the platform 14, which can have lateraldimensions on the order of 100 microns (μm) up to several millimeters,and can also tilt the platform 14 when the upward displacement of theindividual flexible members 16 is unequal. The exact upward displacementand/or angle of tilt of the platform 14 will depend upon the mechanicalforces provided to bend each flexible member 16. Furthermore, theplatform 14 can be tilted in an arbitrary direction with respect to thesubstrate 12 (e.g. for redirecting an incident light beam 200 as shownin FIGS. 1C and 1D), or switched over time between a plurality ofdifferent directions by changing the mechanical forces provided to oneor more of the flexible members 16.

The apparatus 10 of FIGS. 1A and 1B including any MEM actuators 18 canbe formed using conventional surface micromachining of multiplepolycrystalline silicon (also termed polysilicon) layers withintervening sacrificial oxide layers (e.g. comprising silicon dioxide ora silicate glass) on a silicon or silicon-on-insulator substrate (seee.g. U.S. Pat. Nos. 5,631,514 and 6,082,208 which are incorporatedherein by reference for further details of processes for fabricatingsurface micromachined structures having four and five levels ofpolysilicon, respectively).

Those skilled in the art understand that surface micromachining involvesmany processing steps for building up a particular structure for amicroelectromechanical device. These surface micromachining processsteps are based on conventional integrated circuit (IC) processingsteps, including material deposition, photolithography, masking,etching, mask stripping, and cleaning. Up to hundreds of individualprocess steps can be used to form the completed structure of the MEMapparatus 10 based on repeated deposition and patterning of alternatinglayers of polysilicon and the intervening sacrificial oxide, with theapparatus 10 being built up layer by layer. The term “patterning” asused herein refers to a sequence of well-known processing stepsincluding applying a photoresist to the substrate 12, prebaking thephotoresist, aligning the substrate 12 with a photomask, exposing thephotoresist through the photomask, developing the photoresist, bakingthe wafer, etching away the surfaces not protected by the photoresist,and stripping the protected areas of the photoresist so that furtherprocessing can take place. The term “patterning” can further include theformation of a hard mask (e.g. comprising about 500 nanometers of asilicate glass deposited from the decomposition of tetraethylorthosilicate, also termed TEOS, by low-pressure chemical vapor deposition atabout 750° C. and densified by a high temperature processing) overlyinga polysilicon or sacrificial oxide layer in preparation for definingfeatures into the layer by etching.

To briefly summarize the surface micromachining fabrication process usedto construct the MEM apparatus 10, a silicon or silicon-on-insulatorsubstrate 12 can be initially coated with dielectric isolation films oflow-pressure chemical vapor deposition (LPCVD) silicon nitride (about8000 Å thick) over a thermal oxide (about 6300 Å thick). Eachsubsequently deposited and patterned layer of polysilicon or sacrificialoxide can be, for example, in the range of 0.3-2 μm thick, with theexact layer thickness depending upon the particular elements of theapparatus 10 to be fabricated from each layer of polysilicon orseparated by each layer of the sacrificial oxide. The first patternedlayer of polysilicon (termed Poly-0) is generally used to formelectrical interconnections (e.g. wiring between bond pads and the MEMactuators 18 and electrically active portions of the MEM actuators 18,44 and 90) and to form ground planes as needed (e.g. underlying theplatform 14, the flexible member 16, and the elevation members 66). ThePoly-0 layer is not structural and can be relatively thin (about 3000 Å)with phosphorous doping to improve electrical conductivity. Other of thepolysilicon layers can be doped (e.g. by ion implantation) forelectrical conductivity as needed. All mechanical polysilicondepositions are LPCVD fine-grained polysilicon deposited at 580° C.

Up to four additional polysilicon layers can be used as mechanical (i.e.structural) layers to build up the structure of the apparatus 10. Afirst structural polysilicon layer (termed Poly-1) can be used to form asecond electrode 112 of a vertical zip actuator 90, with a superposedfirst electrode 110 being formed from the Poly-0 layer. Alternately, thesecond electrode can be formed by laminating together the Poly-1 layerand a second structural layer termed Poly-2. The Poly-1 and Poly-2layers can also be laminated together with an intervening layer of thesacrificial oxide to form a plurality of pre-stressed members 74 asdescribed hereinafter. The Poly-1 layer can be 1.0 μm thick; and thePoly-2 layer can be 1.5 μm thick. The Poly-2 layer can also be used toform each elevation member 66 which can be, for example, 1.5 μmthick×5-10 μm wide×100-500 μm long. The elevation members 66 can beanchored to the substrate 12 using an anchor point 70 and a flexiblejoint 72 (i.e. a flexure) which can be fabricated, for example, from thePoly-1 layer.

Each flexible member 16 can be formed from a third structural layer ofpolysilicon (termed Poly-3) which can be 2.25 μm thick. The width andlength of each flexible member 16 will depend upon the size of theplatform 14 and the particular embodiment of the present invention inwhich the flexible member 16 is used. Generally, the flexible member 16can have a width in the range of 5-50 μm and a length in the range of100-2000 μm or more depending upon the size of the platform 14 and theamount of elevation or tilt to be provided thereto. The platform 14 canbe formed from either a fourth polysilicon layer (termed Poly-4) whichcan be 2.25 μm thick, or alternately from a combination of the Poly-3and Poly-4 layers laminated together (see e.g. FIG. 4 where arcuatepolysilicon portions 42 and a lower portion 14′ are formed from thePoly-3 layer with the remainder of the platform 14 being formed from thePoly-4 layer). Each compliant member 22 can be formed from the Poly-3 orPoly-4 layers, or from both.

The Poly-0 through Poly-4 layers can be used to build up the structureof the electrostatic comb actuators 44, while the Poly-1 through Poly-4layers can be used to form a yoke 48 and a displacement multiplier 46which can be used together with the actuators 44 to provide the forcerequired to operate the apparatus 10. A plurality of fuses 82 can beformed from the Poly-1 through Poly-3 layers for attaching the platform14 to the substrate 12 during fabrication. Alternately, a plurality ofrestraining clips 88 can be used to secure the platform 14, with therestraining clips 88 being formed, for example, from the Poly-2 throughPoly-4 layers.

The planarity of each layer of polysilicon or sacrificial oxide can bemaintained during build-up of the apparatus 10 by using chemicalmechanical polishing (CMP) as known to the art (see e.g. U.S. Pat. No.5,804,084 which is incorporated herein by reference). Planarization ofthe polysilicon and sacrificial layers used to build up the platform 14using CMP can be advantageous to present a smooth surface topographyespecially when the platform 14 is used to form a mirror for reflectingan incident light beam. Post-deposition annealing of the polysiliconlayers can also be used to minimize internal stress which couldotherwise distort the platform 14 upon a final etch-release step inwhich a solution or vapor comprising hydrofluoric acid (HF) is used toetch away the various sacrificial oxide layers separating andencapsulating the polysilicon layers during build-up of the structure ofthe MEM apparatus 10. Such annealing does not, however, affect elementsof the apparatus 10 which are specially designed to have a built-instress gradient (e.g. pre-stressed members 74).

In the above etch-release step, which can require several hours orovernight, a plurality of micron-sized openings (not shown) can beformed through the various polysilicon layers to permit the HF to reachthe underlying sacrificial oxide. This is especially important forremoval of the sacrificial oxide underneath large-area elements of theapparatus 10 such as the platform 14. After removal of the sacrificialoxide, the micron-sized openings can be optionally plugged by depositionof a layer of silicon nitride using LPCVD.

In the apparatus 10 of the present invention as shown in FIGS. 1A and1B, preferably a trio of flexible members 16 are used since threemembers 16 are adequate to control the elevation and tilt of theplatform 14. These three flexible members 16 can be equidistantly spacedabout the platform 14 (i.e. with a 120° angular separation betweenconnection points to the platform 14) as shown in FIG. 1A. Once theelevation of the platform 14 is established by an appropriate selectionof the forces on the various flexible members 16, the use of a trio offlexible members 16 requires only two electrical signals (i.e.activation voltages) to the MEM actuators 18 providing forces to two ofthe three flexible members 16 in order to tilt the platform 14 to anarbitrary angle with respect to the substrate 12. Tilting of theplatform 14 results from a difference in elevation of the flexiblemembers 16. In some embodiments of the present invention, only a pair offlexible members 16 are required when the platform 14 is anchored to thesubstrate 12 on one side thereof with a flexible hinge 126 (see FIGS.16A and 16B).

To minimize stress on the platform which could otherwise possiblydistort the platform due to bending of the flexible members 16 in theembodiment of the present invention shown in FIGS. 1A and 1B, aresultant vertical force (indicated by the vertical arrow in FIG. 1B)provided from the flexible member 16 is coupled to the platform 14 atits periphery using a compliant member 22. The compliant member 22 canbe, for example, about 1 μm wide×2-6 μm high to provide a stiffness inthe vertical direction that is greater than the stiffness in lateraldirections substantially parallel to the plane of the platform 14. Thisresults in the vertical force being applied in a direction normal to theplane of the platform 14 to lift the platform 14 without any sidewaysstress that could possibly distort or deform the platform 14.Additionally, the compliant member 22 allows for some lateral movementof each flexible member 16 with respect to the platform 14 as the forcesapplied to each member 16 are varied to to elevate or tilt the platform14. Although some rotation of the platform 14 is possible duringelevation or tilting thereof, the three compliant members 22 in FIG. 1Acooperate to minimize any lateral forces applied to the platform 14.

Although the platform 14 is generally fabricated to be planar, theplatform 14 can, under certain circumstances, assume a curved shape(i.e. with a concave or convex upper surface). A concave platform 14 isschematically illustrated in FIG. 1C. The curved shape can result fromstress induced in the platform 14 by deposition of a light-reflectivemirror coating 24 thereon for use in redirecting (i.e. reflecting) anincident light beam 200. The mirror coating 24, which can be applied toany of the embodiments of the apparatus 10 described herein, cancomprise any type of reflective metal coating or dielectric mirrorcoating as known to the art, with the selection of a particular mirrorcoating generally being determined by a particular application of theapparatus 10 which will define the desired reflectivity and thewavelength of the light to be reflected by the mirror coating 24. Thoseskilled in the art will understand that metals such as gold, silver andaluminum can be used to form a reflective metal coating, and that adielectric mirror coating can be formed by alternately depositing layersof a relatively high index of refraction dielectric material (e.g. TiO₂)and a relatively low index of refraction dielectric material (e.g.SiO₂), with each layer having an effective optical thickness ofone-quarter-wavelength (λ/4n where n is the refractive index of thedielectric material forming each layer). Bowing of the platform 14 canarise, for example, from differences in thermal expansion of theplatform 14 and the coating material since the mirror coating isgenerally applied to the platform at an elevated temperature. In somecases, bowing (i.e. curvature) of the platform 14 due to the depositedmirror coating 24 can be used to advantage (e.g. for focusing ordiverging the incident light beam 200); whereas in other cases a planarmirror is required (e.g. for redirecting the incident light beam 200without altering the shape of the beam).

To restore the planarity of the mirror formed by the platform 14 withthe mirror coating 24 thereon, a stress-compensation coating 26 can bedeposited on the opposite side of the platform 14. When the mirrorcoating 24 is applied on a topside of the platform 14, an access opening28 can be formed completely through the substrate 12. This can be done,for example, prior to the etch-release step. The access opening 28 asshown in the schematic cross-section view of FIG. 1D can be formed, forexample, by wet etching inward through the substrate 12 from the bottomthereof using a patterned etch mask (e.g. using an anisotropic wetetchant such as potassium hydroxide, tetramethyl ammonium hydroxide orethylenediamine pyrocatechol which generally produces sloped sidewalls),or alternately by using a deep reactive ion etching process whichcombines multiple anisotropic etching steps with steps forsimultaneously depositing an isotropic polymer/inhibitor to minimizelateral etching and sloping sidewalls. Such a deep etching process isdisclosed in U.S. Pat. No. 5,501,893 to Laermer et al, which isincorporated herein by reference. The stress-compensation coating 26 cancomprise the same material as the mirror coating 24 with generally thesame layer thickness.

The first embodiment of the present invention in FIGS. 1A and 1B isinitially fabricated with the flexible members 16 being flat (i.e.coplanar with the substrate). Forces can then be applied to eachflexible member 16 for buckling thereof upward to elevate the platform14 to a predetermined height. This can be done using the MEM actuators18.

To aid in uplifting the platform 14 and the flexible members 16, one ormore electrostatically activated pry bars 30 can be formed on thesubstrate 12 and partially underlying the platform 14 as shown in FIGS.2A-2C. These pry bars 30 can be formed, for example, from the Poly-3 andPoly-4 layers and can be suspended above the substrate 12 andelectrically grounded to the substrate 12 by support posts 32 andtorsional joints 34. The support posts 32 can be formed from multiplestacked polysilicon layers (e.g. Poly-0 through Poly-4) and thetorsional joints 34 can be formed from a single polysilicon layer (e.g.Poly-3 or Poly-4). The torsional joints 34 can be, for example, 1 μmwide×2 μm high×5 μm long.

A lift electrode 36, which can be formed in the Poly-0 layer, is locatedunderneath the end of each pry bar 30 distal to the platform 14 as shownin FIG. 2B which represents a schematic cross-section view along thesection line 2—2. When an activation voltage (e.g. up to about 300volts) from a source or power supply (not shown) is provided between theelectrically-grounded pry bar 30 and the lift electrode 36, anelectrostatic force of attraction is generated which pulls the distalend of the pry bar 30 downward until it rests on the substrate 12 or onan optional stop 38, thereby displacing the other end of the pry bar 30upward to elevate the platform 14 and the flexible members 16. This isshown schematically in FIG. 2C. The vertical lift provided by the prybars 30 can be, for example, in the range of 5-20 μm with the exactvertical lift depending upon several factors including the appliedactuation voltage, the mechanical advantage (determined by the locationof the torsional joints 34) and the spacing between the pry bar 30 andthe lift electrode 36 or stop 38. A plurality of pry bars 30 uniformlyspaced about the periphery of the platform 14 can be simultaneouslyoperated using a common actuation voltage.

In other embodiments of the present invention, alternate ways ofinitially elevating the platform 14 and flexible members 16 can beprovided. For example, certain embodiments of the present invention asdescribed hereinafter utilize a micromanipulator probe tip to slide amechanical latch 96 forward or backward as needed to initially elevatethe flexible members 16 and platform 14 (see FIGS. 15A and 15B).Alternately, a plurality of pre-stressed members 74 can be provided onthe substrate 12 underneath the platform 14 to initially elevate theplatform 14 and bend the flexible members 16 upwards after theetch-release step (see FIGS. 8A-8C).

FIGS. 3A and 3B schematically illustrate a second embodiment of thepresent invention. This second embodiment of the present invention issimilar to the first embodiment of FIGS. 1A and 1B except that one endof each flexible member 16 is attached to the substrate 12 by an anchor40. The anchor 40 can be formed from the same layer of polysilicon usedto form the flexible member 16 (e.g. by forming a via in an underlyinglayer of the sacrificial oxide prior to depositing the Poly-3 layer forforming the flexible member 16 so that the Poly-3 layer is attached tothe substrate 12 through the underlying polysilicon layers), or can beformed from an additional layer of polysilicon (Poly-0 through Poly-2 ora combination thereof laminated together). The provision of anchor 40 onone end of each flexible member 16 simplifies operation of the apparatus10 since only a single MEM actuator 18 need be used to provide anactuation force to the other end of each flexible member 16. Althoughthe flexible members 16 in the plan views of FIGS. 1A and 3A are shownas being linear (i.e. straight), they can alternately be curved aroundthe periphery of the platform 14 to save space.

The MEM actuator 18 in FIGS. 3A and 3B can be an electrostatic actuatorsuch as a electrostatic comb actuator (see FIG. 6 and U.S. Pat. No.6,133,670 which is incorporated herein by reference) or an electrostaticcapacitive plate actuator (see U.S. Pat. No. 6,211,599 which isincorporated herein by reference), or any other type of electrostaticactuator as known to the art. Those skilled in the art will understandthat the MEM actuator 18 in FIGS. 3A and 3B can also be a thermalactuator.

In the event that a displacement provided by the MEM actuator 18 issmaller than a desired range of lateral motion of the actuated end ofthe flexible member 16, a displacement multiplier 46 can be locatedbetween the MEM actuator 18 and the flexible member 16 (see FIG. 6). Acompliant displacement multiplier 46 operates by lever action toincrease the displacement with a corresponding reduction the actuationforce provided to the flexible member 16. Further details of adisplacement mulitplier 46 suitable for practice of the presentinvention is disclosed in U.S. Pat. No. 6,175,170 to Kota et al, whichis incorporated herein by reference. Alternately, one or more lever armssupported on pin joints or flexible joints can be used as a substitutefor the displacement multiplier 46 to increase the displacement providedby the MEM actuator 18.

Those skilled in the art will also understand that the end of eachflexible member 16 to which the actuation force is applied can beoperatively connected to a MEM actuator 18 that comprises a rack whichis driven to move in the plane of the substrate 12 by an electrostaticmicromotor or an electrostatic rotary actuator. An electrostaticmicromotor-driven rack is disclosed in U.S. Pat. No. 6,082,208 toRodgers et al which is incorporated herein by reference. Anelectrostatic rotary actuator is disclosed in U.S. Pat. No. 6,211,599which is incorporated herein by reference.

In the apparatus 10 of FIGS. 3A and 3B, the exact displacement of theflexible member 16 used to elevate or tilt the platform 14 will dependon the size of the platform 14 and the extent to which the platform 14is to be elevated or tilted. As an example, for a circular platform 14having a radius of 500 μm and a trio of flexible members 16 each about2.1 mm long, a displacement of one of the flexible members 16 by about30 μm can be used to tilt the platform 14 over an angle θ=10° asmeasured between a central axis 20 of the platform 14 and a directionnormal to the substrate 12. Thus, any angle within a cone of 20° angularwidth can be accessed by tilting the platform 14 using one or more ofthe flexible members 16 that are displaced by no more than about 30 μmin one direction or the other. Larger tilt angles, θ, can be achievedwith larger displacements.

FIG. 4 schematically illustrates in plan view a third embodiment of theMEM apparatus 10 of the present invention, with a part of the platform14 being shown cut away to reveal the structure of a lower portion 14′of the platform 14 and the connection of the flexible member 16 to thelower portion 14′ using a compliant member 22. In FIG. 4, the trio offlexible members 16 are arranged symmetrically about a central axis 20of the platform, with each compliant member 16 being connected to thelower portion 14′ of the platform 14 at a point equidistant from thecentral axis 20. A connection point that is located between the centralaxis 20 and the periphery of the platform 14 as shown in FIG. 3 isadvantageous since it increases the elevation or tilt for a givendisplacement of the flexible member 16 as compared to a connection tothe periphery of the platform 14 as shown in the devices 10 of FIGS. 1Aand 1B and FIGS. 2A and 2B.

FIG. 5A schematically illustrates the connection of the flexible member16 to the platform 14 through the lower portion 14′ thereof along thesection line 3—3 in FIG. 4. An upward-directed force provided byflexible member 16 is conveyed through the compliant member 22 and thelower portion 14′ to the platform 14 at its periphery. This minimizesany distortion of the platform 14 that could otherwise possibly occur ifthe flexible member 16 were connected directly to the platform 14 nearthe central axis 20. The lower portion 14′ can be formed from adifferent polysilicon layer (e.g. Poly-3) from the remainder of theplatform 14 which can be formed from the Poly-4 layer. An interveningsacrificial oxide layer (not shown in FIG. 5A) can be used to provide aspacing of, for example, 2 μm between the lower portion 14′ and theremainder of the platform 14.

In FIG. 5A, the compliant member 22 can be formed as avertically-oriented ribbon (e.g. with a width of 1 μm and a height of2.25 μm) to provide a stiffness in the vertical direction that is largerthan the stiffness in the horizontal direction (i.e. the lateraldirection). Although the compliant member 22 is shown herein as beinglinear (i.e. straight), those skilled in the art will understand thatthe compliant member 22 can also be formed with other shapes. Forexample, a serpentine shape (i.e. with a plurality of folds) for thecompliant member 22 can be used to save space while increasing thecompliance in the lateral direction compared to the compliance in thevertical direction. As another example, a pair of compliant members 22can be used to attach opposites sides of a head 16′ of the flexiblemember 16 to the platform 14 (see FIG. 6).

The compliant member 22 is used to convey any vertical displacement ofthe flexible member 16 to the lower portion 14′ and therefrom to theperiphery of the platform 14 which can be stiffened by a plurality ofarcuate polysilicon portions 42 arranged about the central axis 20. Thearcuate polysilicon portions 42 can be formed by depositing the Poly-4layer into arcuate trenches formed in the intervening sacrificial oxidelayer (not shown) so that the Poly-4 layer is laminated with an arcuateportion of the underlying Poly-3 layer.

The structure of the apparatus 10 shown in FIG. 5A allows each MEMactuator 18 to move the platform 14 upward or downward or to tilt theplatform 14 about a predetermined angle without distorting the surfaceof the platform 14. Furthermore, the use of the compliant members 22 forconnecting the flexible members 16 to the platform 14 allows a limitedrange of movement of the flexible members 16 in the lateral direction asthe height of the flexible member 16 is changed. FIGS. 7A and 7B show asmall lateral displacement, ΔL, of the elevated end of the flexiblemember 16 with a change in elevation, Δh, which is due to the other endof the flexible member 16 being displaced in the plane of the substrate12 by an amount Δx. The lateral displacement, ΔL, results in a slightrotation of the platform 14 with a change in elevation or tilt thereof.

In other embodiments of the present invention, the lower portion 14′ canbe omitted and the connection of the MEM actuator 18 and flexiblemembers 16 shown in FIG. 6 can be made to platform 14 or to the arcuatepolysilicon portions 42 by locating the compliant members 22 about theperiphery of the platform 14 as shown in FIGS. 1A, 3A and 16A (e.g. whena stress-compensation coating 26 is to be formed on the underside of theplatform 14 as described previously with reference to FIG. 1D).

In yet other embodiments of the present invention, the platform 14 caninclude a sub-platform 14″ having smaller lateral dimensions than theplatform 14 and centered about the central axis 20 underneath theplatform 14 as schematically illustrated in FIG. 5B. The flexiblemembers 16 can then be connected to the sub-platform 14″ rather thandirectly to the platform 14 or to the lower portion 14′. If thesub-platform 14″ is used, the arcuate polysilicon portions 42 can beoptionally used to stiffen the platform 14.

FIG. 6 shows an enlarged plan view of the MEM actuator 18 in FIG. 4. TheMEM actuator 18 comprises a pair of electrostatic comb actuators 44coupled to drive a compliant displacement multiplier 46 through a yoke48. Each electrostatic comb actuator 44 further comprises a plurality ofmoveable electrostatic combs 50 attached to a rigid framework 52 (i.e. aframe) which can include a truss 54 to concentrate the force produced bythe actuator 44, and a plurality of stationary electrostatic combs 56attached to the substrate 12. Each electrostatic comb 50 and 56 can bebuilt up by conventional surface micromachining from one or more layersof deposited and patterned polysilicon (e.g. 3-4 structural polysiliconlayers with an overall thickness of 4-7 μm). The rigid framework 52 issupported above the substrate 12 by a plurality of springs (not shown)which can be folded underneath the framework 52 to save space. The rigidframework 52 allows the moveable and stationary electrostatic combs, 50and 56, to have interdigitated fingers about 1-2 μm wide and 3-10 μmlong and to be closely spaced (e.g. ≦1 μm between the fingers of the twocombs 50 and 56) so that a relatively large force can be produced byeach electrostatic comb actuator 44 when an actuation voltage (e.g.15-90 V) is provided between the moveable and stationary electrostaticcombs, 50 and 56. The moveable electrostatic combs 50 and the supportingframe 52 are preferably maintained at ground electrical potential by anelectrical connection that can be made through the springs underlyingthe frame 52 to the substrate 12, or to electrical wiring 94 formed bypatterning the Poly-0 layer. Further details of the electrostatic combactuators 44 can be found in U.S. Pat. No. 6,133,670 which isincorporated herein by reference.

Those skilled in the art will understand that other types ofelectrostatic actuators can be used for practice of the presentinvention. For example, capacitive plate electrostatic actuators asdisclosed in U.S. Pat. No. 6,211,599 can be substituted for theelectrostatic comb actuators 44 in the device 10 of FIG. 4.

The rigid structure of the electrostatic comb actuators 44 in FIG. 6generally limits an available output displacement to a few μm (e.g. 2-3μm). Therefore, a compliant displacement multiplier 46 is provided tomultiply the displacement provided by the actuators 44 by apredetermined factor of (e.g. 10-20) that is sufficient to provide apredetermined range of displacement of the flexible member 16 as neededto elevate the platform 14 or to tilt the platform 14 over apredetermined angle. The displacement multiplier 46 comprises an inputend 58 and an output end 60, with a plurality of beams 62 formed frommultiple stacked and interconnected layers of polysilicon (e.g. Poly-1through Poly-4) being connected between the input end 58 and the outputend 60 as shown in FIG. 6, and with some of the beams 62 being anchoredto the substrate 12 by supports 64 and with the remainder of the beams62 being suspended above the substrate 12. Each beam 62 in thedisplacement multiplier 46 can be, for example, about 1-3 μm wide×5-7 μmhigh×50-200 μm long.

The displacement multiplier 46 receives an input displacement (indicatedby the small arrows in FIG. 6) and an input force from the electrostaticcomb actuators 44 through the yoke 48 at the input end 58 and generatesa multiplied output displacement (indicated by the large arrow in FIG.6) and a correspondingly reduced output force at the output end 60 ofthe displacement multiplier 46. The displacement multiplier 46 operatesby directing the input force along certain of the beams 62 and byflexing other of the beams 62 so that a lever action is produced tomultiply the input displacement without the need for any rotating joints(i.e. pin joints). Depending upon the design of the displacementmultipler 46 and the arrangement of the various beams 62, the outputdisplacement can be either 180° out-of-phase with the input displacementas shown in FIG. 6, or in-phase with the input displacement. Furtherdetails of the fabrication and operation of this type of surfacemicromachined displacement multiplier 46 can be found in U.S. Pat. No.6,175,170 which is incorporated herein by reference.

In FIG. 6, movement of the elongate flexible member 16 out of the planeof the substrate 12 is effected by attaching the flexible member 16 nearone end thereof to a pair of juxtaposed elongate elevation members 66through compliant joints 68 which can be about 1 μm wide and formed fromthe Poly-2 or Poly-3 layers. The other end of each elevation member 66is connected to an anchor point 70 on the substrate 12. The anchor point70, which can comprise a flexible joint 72 as shown in FIGS. 7A and 7B,allows each elevation member 66 to be rotated out of the plane of thesubstrate 12 about the anchor point 70 as the end of the flexible member16 connected to the output end 60 of the displacement multiplier 46 ismoved in the plane of the substrate 12 in the direction indicated by thelarge arrow in FIG. 6. The resultant elevation of the end of theflexible member 16 connected to the elevation members 66 out of theplane of the substrate 12 is used to elevate or tilt the platform 14 andis schematically illustrated in the cross-section views of FIGS. 7A and7B taken along the section line 4—4 in FIG. 6.

Those skilled in the art will recognize that the MEM actuator 18 of FIG.6 and other actuators described herein as producing vertical motion canbe used for many different applications of microelectromechanicaldevices wherein a displacement provided by an actuator that issubstantially in the plane of the substrate is to be converted into adisplacement that is in a direction substantially perpendicular to thesubstrate.

In FIG. 7A, the elevation members 66 and the flexible member 16, whichcan be initially fabricated as planar structures by patterning thePoly-2 and Poly-3 layers, respectively, can be initially elevated abovethe substrate 12 with the platform 14. This can be done in several ways.For example, a plurality of elongate pre-stressed members 74 asdescribed in detail hereinafter (see FIGS. 4 and 8A-8C) can befabricated underneath the platform 14 to urge the platform 14 upwardaway from the substrate 12 after the etch-release step and after thesevering of any fuses 86 or disengagement of any restraining clips 88which can be used to initially lock the platform 14 in place. As anotherexample, one or more electrostatically actuated pry bars 30 can be usedto pry the platform 14 and associated flexible members 16 upward awayfrom the substrate 12 as described previously with reference to FIGS.2A-2C. As yet another example, a micromanipular probe tip can be used tooperate a mechanical latch 96 to displace one end of the flexible member16 and to lock that end of the flexible member 16 in place in an initialelevated position, thereby anchoring that end of the flexible member 16to the substrate 12. Such a mechanical latch 96 will be described indetail hereinafter (see FIGS. 12A and 12B and 14A and 14B).

Once the flexible member 16 and elevation members 66 are in theirinitial elevated positions as shown schematically in FIG. 7A, furthermovement of the end of the flexible member 16 connected to the MEMactuator 18 over a distance, Δx, in the plane of the substrate 12(indicated by the horizontal arrow) will result in a further elevation,Δh, of the other end of the flexible member 16 as shown in FIG. 7B. Thisincrease in elevation results from the elevation members 66 beingrotated about the anchor point 70 while being flexibly connected to themember 16 by the compliant joints 68. By controlling the voltagesapplied to each MEM actuator 18 in FIG. 4, which comprises a pair of theelectrostatic comb actuators 44 operating in tandem, the elevation ortilt of the platform can be controlled and changed. For example, for a1600 μm long flexible member 16 initially elevated to a height of 350 μmand connected to a pair of elevation members 66 which are each 800 μmlong, movement of the end of the flexible member 16 connected to the MEMactuator 18 by a distance Δx=50 μm will result in a change in elevationof Δh of approximately 175 μm. A 175 μm change in elevation on one sideof a 1000 μm wide platform 14 can be used to produce a 10° tilt of theplatform 14.

FIGS. 8A-8C illustrate formation of the pre-stressed members 74 used inFIG. 4 for the initial elevation of the platform 14 and elementsconnected thereto. FIG. 8A shows a plan view of one of the pre-stressedmembers 74 during fabrication and prior to the etch-release step, withthe pre-stressed member 74 being embedded in layers of a sacrificialoxide 76 and anchored at one end thereof to the substrate 12.

Cut-away views in FIGS. 8A and 8B show the structure of the pre-stressedmember 74 which comprises an elongate core 78 of an oxide material,which generally has the same composition as the sacrificial oxide 76 andwhich can be, for example, 0.5 μm thick, completely encased within apolysilicon body 80 which can be formed from a pair of deposited andpatterned polysilicon layers (e.g. the Poly-1 layer which can be 1 μmthick, and the Poly-2 layer which can be 1.5 μm thick) that areconnected together through an annular trench formed in the interveninglayer of the sacrificial oxide 76 (i.e. by depositing the Poly-2 layerin the trench and thereby connecting the Poly-2 layer to the Poly-1layer at the edges of the pre-stressed member 74).

By being completely encased within the polysilicon body 80, the core 78is not removed during the etch-release step which etches away theremainder of the sacrificial oxide 76. As a result, a stress gradientproduced along the thickness of the pre-stressed member 74 by thecombination of the oxide material in the core 78 and the polysiliconbody 80, which have different layer thicknesses on each side of theoxide core 78, acts to bend the unanchored end of the pre-stressedmember 74 out of the plane of the substrate 12 to accommodate the stressgradient when the surrounding sacrificial oxide 76 is removed during theetch-release step. Each pre-stressed member 74 thus forms a compressedspring which provides an upward-directed force on the overlying platform14 to urge the platform 14 to move upward and away from the substrate12. The pre-stressed members 74 need not be attached to the platform 14.In other embodiments of the present invention, the pre-stressed member74 can be formed as a spiral to form a compressed coiled spring uponrelease by removing the surrounding sacrificial oxide 76. Although thepre-stressed members 74 are shown located beneath the platform 14 tosave space, in other embodiments of the present invention, thepre-stressed members 74 can be located at least partially outside theplatform 14 with the unanchored end of each pre-stressed member 74contacting the underside of the platform 14 to urge it upward.

Generally, it is preferable to have the platform 14 secured to thesubstrate 12 during the etch-release step and immediately afterwards.This is advantageous to prevent possible adhesion of the platform 14 tothe substrate 12 during the etch-release step, or to permit depositionof a mirror coating 24 on the platform after the etch-release step. Oneway of securing the platform 14 to the substrate 12 is by providing aplurality of fuses 82, which can be arranged in pairs as shown in FIG. 4to anchor the platform 14 to the substrate 12. To release the platform14 for movement, the fuses 82 can be electrically severed. Alternately,a plurality of removable restraining clips 88 can be used to secure theplatform 14 in place until the clips 88 are electrically or mechanicallydisengaged (see FIGS. 10A and 10B).

FIGS. 9A and 9B show schematic cross-section views along the sectionline 5—5 in FIG. 3 before and after electrical severing of the fuses 82,respectively, to illustrate operation of the fuses 82 which can be usedto hold the platform 14 securely in place during the etch-release step.In FIG. 9A, each fuse 82 comprises an electrical probe pad 84 insulatedfrom the substrate 12 by the thermal oxide and silicon nitride layers(not shown) initially formed on the substrate 12 as describedpreviously. A fusible link 86 (i.e. a filament) connects each probe pad84 to the periphery of the platform 14. This can be done, for example,by connecting each fusible link 86 to one of the arcuate polysiliconportions 42 or alternately to the underside of the platform 14 near theperiphery. Each fusible link 86 can have cross-sectional dimensions of,for example, about 1-1.5 μm and a length of 20 μm. The probe pads 84 canbe formed from the plurality of deposited and patterned layers ofpolysilicon (e.g. Poly-1 through Poly-3), while the fusible links 86 canbe formed from a single layer of polysilicon (e.g. Poly-2 or Poly-3).

FIG. 9B shows the result of electrically severing each pair of fuses 82supporting the platform 14. This electrical severing process (i.e.blowing the fusible links 86) can occur when a sufficiently largevoltage or voltage pulse (e.g. up to 300 V) from a source or powersupply (not shown) is applied across each pair of probe pads 84, oralternately between each probe pad 84 and the platform 14 which ismaintained at ground electrical potential. The applied voltage orvoltage pulse produces an electrical current sufficiently large to blow(i.e. melt or vaporize) each fusible link 86. When the fuses 82 securingthe platform 14 to the substrate 12 are severed, the platform 14 is freeto move upward away from the substrate 12 due to the action of theunderlying pre-stressed members 74. The initial elevation of theplatform 14 will depend upon the length and force of the pre-stressedmembers 74, and can be, for example, up to about one-third of the widthof the platform 14. At this point, the elevation or tilt of the platformcan be controlled and changed using the MEM actuators 18 as describedpreviously.

Locating the fusible links 86 at a level lower than the platform can beadvantageous to prevent the vaporized or melted polysilicon from thesevered links 86 from being deposited on the upper surface (i.e. thetopside) of the platform 14, especially when a mirror coating 24 hasbeen provided on the platform 14 to increase its reflectivity to light.Additionally, it can be advantageous to sever the fusible links 86 usingvoltages of different polarity applied to each probe pad 84 (e.g. usinga positive voltage or voltage pulse applied to one probe pad 84 and anegative voltage or voltage pulse applied to the other probe pad 84 ofeach pair of fuses 82). This can be done, for example, using analternating-current (ac) power supply or pulse generator coupled to aprimary coil of a transformer having a secondary coil with a center-tapconnection to provide two opposite-polarity output voltage waveforms orpulses when the center-tap connection is electrically grounded. Theprovision of the opposite-polarity voltages or voltage pulses to eachprobe pad 84 can mitigate effects due to parasitic capacitance orparasitic current paths in the apparatus 10 and ensure thatsubstantially the same electrical current is experienced at the sametime in each fuse 82 of a particular pair. The exact magnitude of thevoltages or voltage pulses will depend upon the dimensions of thefusible links 86 and can be learned from practice of the presentinvention.

FIGS. 10A and 10B schematically illustrate, in cross-section view alongthe section line 6—6 in FIG. 11, an alternate way of attaching theplatform 14 to the substrate 12 using a plurality of removablerestraining clips 88 located about the periphery of the platform 14.Each restraining clip 88 can be formed from a plurality of layers of thedeposited and patterned polysilicon (e.g. Poly-2 through Poly-4) duringbuild-up of the apparatus 10, with a thin (e.g. 0.2-2 μm) layer of thesacrificial oxide (not shown) separating the restraining clip 88 fromthe platform 14 during fabrication of the apparatus 10. The sacrificialoxide is removed during the etch-release step leaving a narrow air gapbetween each restraining clip 88 and the platform 14.

To release the platform 14 for upward movement after the etch-releasestep, each restraining clip 88 can be slid away from the platform 14 asshown in FIG. 10B. This can be done, for example, by forming anelectrostatic comb actuator 44 connected to each restraining clip 88 asshown in FIG. 11. Upon activation by applying a voltage across a pair ofprobe pads 92, the actuator 44 moves the restraining clip 88 away fromthe platform 14 thereby releasing the platform 14 to move upward by theaction of the underlying pre-stressed members 74. When the actuationvoltage is removed, the restraining clip 88 moves back to its initialposition, but now underlies the platform 14 which has been elevated. Theprobe pads 92 in FIG. 11, which can comprise a deposited metallization,are connected to the electrostatic comb actuators 44 used to actuate therestraining clips 88 by interconnect wiring 94 which can be formed bypatterning the Poly-0 layer. In other embodiments of the presentinvention, the restraining clips 88 can be operatively connected to amechanical latch 96 as described hereinafter and moved away from theplatform 14 using a micromanipulator probe tip.

FIG. 11 shows a schematic plan view of a fourth embodiment of the MEMapparatus 10 of the present invention. In FIG. 11, a plurality of MEMelectrostatic actuators are spaced about a polygonal platform 14 whichcan be hexagonal in shape, with each electrostatic actuator in thisembodiment being a vertical zip electrostatic actuator 90. A pluralityof restraining clips 88 are spaced about the platform 14 to secure theplatform 14 as previously described, although those skilled in the artwill understand that fuses 82 described previously with reference toFIGS. 4 and 9A-9B can be substituted for the restraining clips 88.

FIGS. 12A and 12B show enlarged plan views of the vertical zip actuator90 of FIG. 11 which can be used to control the elevation and/or tilt ofthe platform 14 in the fourth embodiment of the present invention. FIG.12A shows the vertical zip actuator 90 in an as-fabricated positionimmediately after the etch-release step, with the various layers ofstructural polysilicon used to form the actuator 90, the flexible member16 and the elevation members 66 all being coplanar with the substrate12. FIG. 12B shows the vertical zip actuator 90 in an operating position(i.e. the initial elevated position) with the flexible member 16 and theelevation members 66 being bent upwards out of the plane of thesubstrate 12. This can be done by an operator using a micromanipulatorprobe (not shown) to slide the mechanical latch 96 that is connected tothe vertical zip actuator 90 and the members 16 and 66 from the initialfabricated position as shown in FIG. 12A into a locked position as shownin FIG. 12B.

The mechanical latch 96 comprises a moveable body 98 with a first set ofbarbs 100 and one or more holes 102 sized to receive the tip of themicromanipulator probe. A pair of guides 104 attached to the substrate12 enable movement of the body 98 in a preferred direction (indicated bythe arrow in FIG. 12A). The latch 96 further includes a stationary body106 which is attached to the substrate 12 and has a second set of barbs108 which engage the first set of barbs 100 to anchor the vertical zipactuator 90 and the flexible member 16 to the substrate 12 in theoperating position as shown in FIG. 13A which is a schematiccross-section view along section line 7—7 in FIG. 12B. Further elevationor tilting of the platform 14 can then be performed electrically byproviding an actuation voltage from a source or power supply to thevertical zip actuator 90. In FIGS. 12A and 12B, the mechanical latch 96can be formed from the same polysilicon layers used to form theremainder of the apparatus 10 (e.g. the body 98 can be formed fromPoly-2 and Poly-3; the barbs 100 and 108 can be formed from Poly-2,Poly-3 or both; and the guides 104 can be formed from Poly-1 throughPoly-4).

The vertical zip actuator 90 in FIGS. 12A and 12B comprises one or morefirst electrodes 110 supported on the substrate 12 (e.g. formed in thePoly-0 layer and insulated from the substrate 12 by the interveningsilicon nitride and thermal oxide layers), and a second electrode 112superposed above the first electrodes 110 (e.g. formed from Poly-1,Poly-2 or Poly-3) and anchored to the substrate 12 through themechanical latch 96. Each first electrode 110 can be connected to aseparate bond pad 92 (not shown) through wiring 94 which can be formedby patterning the Poly-0 layer to allow separate addressing and controlof each first electrode 110. The second elctrode 112 can be maintainedat ground electrical potential by an electrical connection to thesubstrate 12 through the flexible member 16 and the elevation members66.

The vertical spacing between the first and second electrodes, 110 and112, varies along the length of the actuator 90 as shown schematicallyin FIG. 13A. The application of an actuation voltage between the one ormore of the first electrodes 110 and the second electrode 112 producesan electrostatic force of attraction along a portion of the actuator 90as indicated by the multiple vertical arrows in FIG. 13B. This force ofattraction urges the second electrode 112 towards the first electrode110, with the shape assumed by the second electrode 112 being determinedby the magnitude and location of the force of attraction. As the secondelectrode 112 moves downwards, it exerts a force on the end of theflexible member 16 to which it is connected, thereby moving the otherend of the flexible member 16 upward by a distance, Δh, as shown in FIG.13B and pivoting the elevation members 66 about the anchor point 70 towhich they are connected by the flexible joint 72. The exact upwardmovement of the flexible member 16, which is responsible for elevatingor tilting the platform 14, will depend upon the number and location ofthe first electrodes 110 being activated and upon the magnitude of theactuation voltage (e.g. 10-200 volts). To prevent electrical shortcircuiting of the first and second electrodes 110 and 112, a pluralityof tabs 114 can be formed on the sides of the second electrode 112 toengage with stops 116 formed on the substrate 12 (e.g. comprising adeposited and patterned layer of silicon nitride) to limit furtherdownward movement of the second electrode 112 and establish a minimumseparation distance between the electrodes 110 and 112.

An advantage of providing a plurality of first electrodes 110 is thatthe elevation or tilt of the platform 14 can be precisely and repeatablycontrolled by addressing one or more of the first electrodes 110 with afixed-magnitude actuation voltage. This can be useful, for example, whena mirror coating 24 is provided on the upper surface of the platform 14in the device 10 of FIG. 11 for redirecting an incident light beam 200from an input optical fiber (not shown) to a particular output fiber(not shown) contained within an array or bundle of output opticalfibers. Each individual optical fiber in the output array or bundle canbe addressed by selecting a particular set of first electrodes 110 whichupon actuation will provide the required angle of tilt needed toredirect the incident light beam 200 from the input optical fiber to theselected output optical fiber. This establishes a line of communicationbetween the input optical fiber and the output optical fiber forinformation transfer. Establishing and switching different lines ofcommunication over time can be performed electronically using acomputer, thereby providing a high-speed optical signal routingcapability which is useful for local area networks or long distancetelephone and data communications.

In some cases, it is desirable for reliability considerations to preventcontact between the second electrode 112 and any other element (e.g. thestops 116) of the apparatus 10 since such contact can possibly lead toadhesion of the contacting elements. An alternative vertical zipactuator 90 which is contact-free is shown schematically in FIGS.14A-14C. Here, a plurality of second electrodes 112 can be supported ona framework comprising a pair of flexible rails 118 to which the secondelectrodes 112 are attached with torsional springs 120. The frameworkcan be anchored to the substrate 12 and electrically grounded through amechanical latch 96, or alternately through one or more support posts.In FIG. 14A, a plurality of openings 122 are formed in each secondelectrode 112, with each opening 122 being sized slightly larger than amating first electrode 110. Contact between the first electrodes 110 andthe second electrodes 112 is avoided since each first electrode 110 fitsinto one of the openings 122 in a superposed second electrode 112.

The first electrodes 110 can be slightly offset from the openings 122 asshown in FIGS. 14B and 14C to provide a gap labelled “A” on a left sideof each first electrode 110 that is smaller than a gap labelled “B” onthe right side of the electrode 110. As an example, the gap “A” can be 1μm when the gap “B” is 1.5 μm. The narrower gap “A” will generate astronger horizontal component to the electrostatic force of attractionthan will be generated at the gap “B” when an actuation voltage isapplied between the first and second electrodes, 110 and 112. This forcewill act to pull the second electrodes 112 and rails 118 to the rightthereby putting these elements in tension thereby preventing any saggingof the second electrodes 112.

Increasing the magnitude of the actuation voltage pulls the secondelectrodes 112 downward towards their corresponding first electrodes 110as shown in FIGS. 14A and 14B. When the contact-free vertical zipactuator 90 is operatively connected to one end of the flexible member16 as shown in FIGS. 13A and 13B, this motion of the actuator 90 can beused to change the elevation of the other end of the flexible member 16.Once sufficient actuation voltage has been applied to align a particularset of electrodes 110 and 112 (i.e. a second electrode 112 and the fourcorresponding first electrodes 110 in FIG. 14A) in the same plane, theelectrostatic force of attraction is greatest so that no furtherdownward movement of that second electrode 112 will occur. Increasingthe actuation voltage will bring additional second electrodes 112 intoalignment with their corresponding first electrodes 110 until all theelectrodes 110 and 112 are coplanar as shown in FIG. 14C. Supporting thesecond electrodes 112 with the torsional springs 120 increases theflexibility of the rails 118 and permits limited torsional motion of thesecond electrodes 112.

In a fifth embodiment of the apparatus 10 of the present invention shownschematically in FIGS. 15A-15C, a pair of vertical zip actuators 90 canbe connected together end to end to form an apparatus 10 similar to thatof FIGS. 1A and 1B except with vertically-directed actuation forces.FIG. 15A shows a schematic plan view of the fifth embodiment of theapparatus 10 after fabrication of the device with each element beingsubstantially coplanar with the substrate. In the schematic side view ofFIG. 15B, the platform 14 can be raised to its initial elevated positionby using a micromanipulator probe to actuate each mechanical latch 96and move the body 98 therein so that the barbs 100 move past a pair ofposts 124 to lock the vertical zip actuator 90 in the operatingposition. This movement of the mechanical latch 96, which is directedopposite that described previously with reference to FIGS. 12A and 12B,compresses the flexible member 16 thereby elevating the member 16 out ofthe plane of the substrate 12 and raising the platform 14 as shown inFIG. 15B. A plurality of pre-stressed members 74 as described previouslycan optionally be located underneath the platform 14 to aid in raisingthe platform 14 to the initial elevated position (see FIGS. 4 and8A-8C). Alternately, a plurality of pry bars 30 can be located about theplatform 14 to aid in elevating it.

In FIG. 15C, once the platform 14 has initially been elevated to anoperating position, further elevation or tilt of the platform 14 cangenerated by applying an actuation voltage to each connected pair ofvertical zip actuators 90 thereby changing the height of one or more ofthe flexible members 16. This actuation voltage can be applied betweenthe first and second electrodes, 110 and 112, with the second electrodesgenerally being held at ground electrical potential by being connectedto the substrate 12. Changing the activation voltage produces avertically-directed electrostatic force of attraction (indicated by themultiple downward-directed arrows in FIG. 15C) between the first andsecond electrodes, 110 and 112, which moves the flexible member 16downward thereby decreasing the elevation of the side of the platform 14to which the flexible member 16 is connected by the compliant member 22.Similarly, decreasing the actuation voltage reduces the force ofattraction and raises the flexible member 16 which behaves like a leafspring. The angle of tilt of the platform 14 and the direction of thecentral axis 20 thereof can be controlled by addressing different pairsof the vertical zip actuators 90 with the same or different actuationvoltages. Multiple first electrodes 110 can be optionally provided foreach vertical zip actuator 90 as described previously with reference toFIGS. 13A and 13B. In other embodiments of the apparatus 10 of thepresent invention, the vertical zip actuators 90 can be formed asdescribed with reference to FIGS. 14A-14C.

FIGS. 16A and 16B show a schematic plan view and a side view,respectively, of a sixth embodiment of the apparatus 10 of the presentinvention which can be used to form a tiltable platform 14 without eachside of the platform 14 being initially elevated above the substrate 12by a significant fraction of the width of the platform 14. In thisembodiment of the invention, the platform 14 is attached to thesubstrate 12 on one side by one or more flexible hinges 126 which areanchored to the substrate 12. Each hinge 126 can be, for example, 1-2 μmthick and wide and 5-50 μm long, and can have a serpentine shape to savespace. The hinges 126 can be formed, for example, from the Poly-2 orPoly-3 layers and anchored to the substrate 12 through the underlyingpolysilicon layers.

The provision of the flexible hinges 126 on one side of the platform 14allows the platform 14 to be tilted using only two MEM actuators 18. TheMEM actuators 18, which can be electrostatic comb actuators 44 as shownin FIG. 6, are connected to the periphery of the platform 14 through apair of compliant members 22. The MEM actuators 18 can be operated intandem to tilt the platform 14 in a single direction, with the centralaxis 20 of the platform 14 defining a plane of tilt angles (i.e. a rangeof tilt angles aligned in a plane that will generally be substantiallyperpendicular to the plane of the substrate 12). Alternately, the MEMactuators 18 can be independently operated to permit tilting of theplatform 14 in two orthogonal directions, thereby defining a cone oftilt angles (i.e. a range of tilt angles falling within a cone).

The platform 14 can optionally include a mirror coating 24, astress-compensation coating 26 or both as described previously withreference to FIGS. 1C and 1D. With a mirror coating 24, the apparatus 10of FIGS. 16A and 16B can be used to form a tiltable mirror or a pop-upmirror for use in redirecting a light beam 200. An array of devices 10can be formed on a common substrate for use in optical switching or beamscanning applications.

To secure the platform 14 in FIGS. 16A and 16B to the substrate 12immediately after the etch-release step, a plurality of fuses 82 ormechanical latches 88 can be provided about the periphery of theplatform 14 as described previously. Also, to aid in initially elevatingthe platform 14 out of the plane of the substrate 12, a plurality ofpre-stressed members 74 can be located underneath the platform 14 asdescribed with reference to FIGS. 4 and 8A-8C. Alternately, a pluralityof electrostatically actuated pry bars 30 can be formed about theplatform 14 as described with reference to FIGS. 2A-2C. It should benoted that generally only a pair of the fuses 82, latches 88 or pry bars30 are needed since the flexible hinge 126 anchors one side of theplatform 14 to the substrate 12.

Other embodiments of the present invention are possible based on theteachings herein. For example, a vertical zip actuator 90 can beconnected between the displacement multiplier 46 and the flexible member16 in the device 10 of FIG. 4 so that the electrostatic comb actuators44 can be used to initially elevate the platform 14 by pulling on oneside of the vertical zip actuators 90 and the flexible member 16. Thisis shown schematically in FIG. 17 as a seventh embodiment of theapparatus 10 of the present invention. The vertical zip actuators 90 canthen be used to provide fine adjustments to the elevation or tilt of theplatform 14, or to provide addressing for precise and repeatablepositioning of the platform 14.

Furthermore, those skilled in the art will understand that a pluralityof devices 10 can be formed on a common substrate 12 and arrayed to forma plurality of platforms 14 that can be elevated or tilted (e.g. forredirecting a plurality of incident light beams 200). The plurality ofdevices 10 can be arranged so that the MEM actuators 18 for one device10 at least partially underlie the platform 14 of the same or adifferent device 10 (e.g. to increase a fill factor of an array ofmirrors formed by the devices 10). Square or hexagonal platforms 14 canbe used in the array to provide a close-packed arrangement with a highfill factor. Such an apparatus comprising a plurality of devices 10 hasapplications for forming a programmable array of mirrors (also termedmicromirrors) for use in forming a projection display, or for use inredirecting or switching a plurality light beams in free space orbetween optical fibers. An array of programmable mirrors also hasapplications for forming a large-area deformable mirror (e.g. to correctphase abberations, or to process one or more light beams).

Other applications and variations of the present invention will becomeevident to those skilled in the art. For example, the apparatus 10 canbe used to support a lens or diffractive optical element on the platform14 to transmit light through an opening in the platform 14. Such adevice 10 has applications for forming a focusing lens mount in whichall flexible members can be operated in unison to change the elevationof the platform without tilting thereof. A focusing lens mount formed bythe apparatus 10 is useful, for example, in a device for reading out orrecording information on a compact disk (CD), or on a digital video disk(DVD). As another example, the apparatus 10 can be used to support anoptical polarizer on the platform 14, with the platform 14 beingrotatable over an angle by a displacement of one or more of the flexiblemembers 16 (see FIGS. 7A and 7B), thereby rotating the optical polarizerand controlling the polarization of an incident light beam 200transmitted through the optical polarizer. The intensity of the incidentlight beam 200 can also be controlled by placing a second linearpolarizer in the path of the incident light beam 200 so that apolarization axis of the second linear polarizer differs from that ofthe polarizer supported on the platform 14.

The matter set forth in the foregoing description and accompanyingdrawings is offered by way of illustration only and not as a limitation.The actual scope of the invention is intended to be defined in thefollowing claims when viewed in their proper perspective based on theprior art.

What is claimed is:
 1. A microelectromechanical apparatus, comprising:(a) a substrate; (b) a platform supported above the substrate by a trioof flexible members, with each flexible member being connected to theplatform by a compliant member, and with an end of each flexible memberconnected to the compliant member further being connected to a pair ofelongate elevation members further being anchored to the substrate; and(c) means for bending each flexible member, thereby changing theelevation or tilt of the platform.
 2. The apparatus of claim 1 whereinthe substrate comprises silicon.
 3. The apparatus of claim 1 wherein theplatform comprises monocrystalline or polycrystalline silicon.
 4. Theapparatus of claim 1 wherein each flexible member is equidistantlyspaced about the platform.
 5. The apparatus of claim 1 wherein anotherend of each flexible member is anchored to the substrate.
 6. Theapparatus of claim 1 wherein the platform is circular or polygonal. 7.The apparatus of claim 1 wherein the platform is planar.
 8. Theapparatus of claim 1 wherein the platform has a curved surface.
 9. Theapparatus of claim 1 wherein a surface of the platform includes a mirrorcoating.
 10. The apparatus of claim 9 wherein another surface of theplatform includes a stress-compensation coating formed thereon.
 11. Theapparatus of claim 1 wherein the means for bending each flexible membercomprises a microelectromechanical actuator operatively connected to theflexible member.
 12. The apparatus of claim 11 wherein themicroelectromechanical actuator comprises an electrostatic actuator. 13.The apparatus of claim 1 wherein the pair of elevation members areanchored to the substrate by a flexible joint.
 14. Amicroelectromechanical apparatus, comprising: (a) a substrate; (b) aplatform supported above the substrate by a trio of flexible members,with each flexible member being connected to the platform by a compliantmember which is connected at one end thereof near a midpoint of one ofthe flexible members, and is connected at the other end thereof to anouter edge of the platform; and (c) means for bending each flexiblemember, thereby changing the elevation or tilt of the platform.
 15. Amicroelectromechanical apparatus, comprising: (a) a substrate; (b) aplatform supported above the substrate by a trio of flexible members,with each flexible member being connected to the platform at one endthereof by a compliant member which is connected at one end thereofproximate to an end of one of the flexible members, with the other endof each compliant member being connected to the platform at a pointequidistant from a central axis of the platform; and (c) means forbending each flexible member, thereby changing the elevation or tilt ofthe platform.
 16. A microelectromechanical apparatus, comprising: (a) asubstrate; (b) a platform supported above the substrate by a trio offlexible members; and (c) an electrostatic comb actuator for bendingeach flexible member, thereby changing the elevation or tilt of theplatform, with the electrostatic comb actuator further comprising aplurality of stationary electrostatic combs attached to the substrateand a plurality of moveable electrostatic combs attached to a framesupported above the substrate, with the moveable electrostatic combsbeing moveable towards the stationary electrostatic combs in response toan actuation voltage provided therebetween.
 17. A microelectromechanicalapparatus, comprising: (a) a substrate; (b) a platform supported abovethe substrate by a trio of flexible members; and (c) an electrostaticvertical zip actuator for bending each flexible member, thereby changingthe elevation or tilt of the platform, with the vertical zip actuatorfurther comprising at least one first electrode supported on thesubstrate and a second electrode superposed above the first electrodewith a spacing between the first and second electrodes being variablealong the length of the superposed first and second electrodes, and withthe second electrode being moveable towards the first electrode inresponse to an actuation voltage provided therebetween.
 18. Theapparatus of claim 17 wherein one end of the second electrode isconnected to the flexible member, and the other end of the secondelectrode is anchored to the substrate.
 19. A microelectromechanicalapparatus, comprising: (a) a substrate; (b) a platform supported abovethe substrate by a trio of flexible members; (c) a plurality ofpre-stressed members underlying the platform, with each pre-stressedmember being anchored at one end thereof to the substrate, and with theother end of each pre-stressed member providing a force on the platformto urge the platform upward from the substrate; and (d) means forbending each flexible member, thereby changing the elevation or tilt ofthe platform.
 20. The apparatus of claim 19 wherein each pre-stressedmember comprises an oxide material encased within a polysilicon body forproducing a stress gradient in the pre-stressed member.
 21. Amicroelectromechanical apparatus, comprising: (a) a substrate; (b) aplatform supported above the substrate by a trio of flexible members;(c) a plurality of restraining clips for holding the platform in placeduring fabrication thereof, with the restraining clips being moveableaway from the platform to release the platform for movement thereof; and(d) means for bending each flexible member, thereby changing theelevation or tilt of the platform.
 22. A microelectromechanicalapparatus, comprising: (a) a substrate; (b) a platform supported abovethe substrate by a trio of flexible members; (c) a plurality of fusesanchoring the platform to the substrate during fabrication thereof, witheach fuse being electrically severable to release the platform formovement; and (d) means for bending each flexible member, therebychanging the elevation or tilt of the platform.
 23. The apparatus ofclaim 22 wherein each fuse comprises polycrystalline silicon.
 24. Amicroelectromechanical apparatus, comprising: (a) a substrate; (b) aplatform supported above the substrate by a plurality of flexiblemembers, with each flexible member being attached to the platform at apoint between a central axis of the platform and the periphery of theplatform; and (c) a plurality of electrostatic actuators providingmovement in a direction substantially in the plane of the substrate,with each electrostatic actuator being operatively connected to one ofthe flexible members to bend the flexible member out of the plane of thesubstrate, thereby elevating or tilting the platform.
 25. The apparatusof claim 24 further including a mirror coating on the platform forreflecting an incident light beam.
 26. A microelectromechanicalapparatus, comprising: (a) a substrate; (b) a platform formed on thesubstrate and having a central axis oriented at an angle to the plane ofthe substrate; (c) a plurality of compliant members, each connected at afirst end thereof to an underside of the platform, with the plurality ofcompliant members further being arranged symmetrically about the centralaxis; (d) a plurality of elongate flexible members, each connected at aninner end thereof to a second end of one of the compliant members, withan outer end of each elongate flexible member being operativelyconnected to an electrostatic actuator; and (e) at least one elongateelevation member connecting each flexible member to the substrate, witheach elevation member acting in combination with the flexible member towhich the elevation member is connected to elevate or tilt the platformin response to a force provided on the outer end of the flexible memberby the electrostatic actuator.
 27. The apparatus of claim 26 wherein thesubstrate comprises silicon.
 28. The apparatus of claim 26 wherein theplatform is circular or polygonal.
 29. The apparatus of claim 26 whereinthe platform includes a stress compensation coating formed thereon. 30.The apparatus of claim 26 wherein the platform includes a mirror coatingon a surface thereof.
 31. The apparatus of claim 30 wherein the othersurface of the platform includes a stress-compensation coating formedthereon.
 32. The apparatus of claim 26 wherein the plurality of flexiblemembers comprises a trio of flexible members.
 33. The apparatus of claim26 further including a plurality of pre-stressed members located beneaththe platform, with each pre-stressed member being anchored at one endthereof to the substrate, and with the other end of each pre-stressedmember providing an upward-directed force on the underside of theplatform to urge the platform upward from the substrate.
 34. Theapparatus of claim 33 wherein each pre-stressed member is elongate andis oriented radially outward along a line from the central axis.
 35. Theapparatus of claim 26 further including a plurality of polysilicon fusesfor securing the platform to the substrate, with each fuse beingelectrically severable to release the platform for movement.
 36. Theapparatus of claim 26 further including a plurality of restraining clipsfor securing the platform to the substrate, with each restraining clipbeing removable to release the platform for movement.
 37. Amicroelectromechanical apparatus, comprising: (a) a substrate; (b) aplatform supported above the substrate by a plurality of elongateflexible members; (c) at least one elevation member connected at one endthereof to each flexible member, with the other end of the elevationmember being anchored to the substrate through a flexible joint; and (d)an electrostatic actuator operatively connected to the other end of eachflexible member to provide a force to the flexible member, therebybending the flexible member and elevatating or tilting the platform. 38.The apparatus of claim 37 wherein the flexible members are spaced by anangle of 120 degrees about a central axis of the platform.
 39. Theapparatus of claim 37 wherein each flexible member supports the platformby a compliant member which connects the flexible member to theplatform.
 40. The apparatus of claim 37 wherein the plurality ofelongate flexible members comprises two or three flexible members. 41.The apparatus of claim 37 wherein one side of the platform is anchoredto the substrate by a flexible hinge.
 42. The apparatus of claim 37wherein the platform includes a mirror coating on a topside thereof.